Process for obtaining cellulosic fiber bundles at least 2.5 cm long from plant stalk rind

Abstract

Novel fiber bundles may be produced as a by-product of sugar cane or other plants. These fiber bundles may be spun into a yarn, or formed into a non-woven mat. The non-woven mat is useful, for example, as a biodegradable geotextile for inhibiting erosion while allowing plants to become established on roadsides, or in other applications. Sugar cane fiber bundles were extracted from the Tilby-separated rind of cane stalks using alkaline treatments. The amount of lignin removed was dependent on alkaline concentration and time, pressure of treatment, and steam explosion conditions if employed. Agitation and vigorous boiling affected the lignin removal. Alkali concentration significantly affected the mechanical properties of the fiber bundles. Tenacity, toughness, and linear density were higher for the fibers extracted at lower alkali concentration. Bending rigidity and hysteresis of these fibers were also higher. This process is also expected to work with other plant stalks having a high lignin content.

We claim: 
     
       1. A process for obtaining cellulosic fiber bundles at least 2.5 centimeters long from lengths of sugar cane rind, comprising the simultaneous steps of: (a) partially delignifying the rind; and   (b) subjecting the rind to limited mechanical action; wherein said partial delignifying step and said limited mechanical action step suffice to obtain cellulosic fiber bundles from the rind, but are insufficient to reduce the cellulosic fiber bundles to ultimate fiber cells; and   wherein sufficient lignin remains in the cellulosic fiber bundles following said partial delignifying step and said limited mechanical action step to bind the fiber cells into fiber bundles at least 2.5 centimeters long.     
     
     
       2. A process as recited in claim 1, wherein said partial delignifying step comprises treating the rind with alkali and heat. 
     
     
       3. A process as recited in claim 1, wherein said limited mechanical action step comprises oscillatory agitation, vigorous boiling, rapid passage of gas bubbles through the rind, or passage through a rotating helical screw. 
     
     
       4. A process as recited in claim 1, wherein said partial delignifying step comprises treating the rind with alkali and heat; and wherein said limited mechanical action step comprises oscillatory agitation, vigorous boiling, rapid passage of gas bubbles through the rind, or passage through a rotating helical screw. 
     
     
       5. A process as recited in claim 1, wherein said limited mechanical action step comprises impregnating the rind with steam; and abruptly reducing the pressure applied to the rind, at a temperature above the boiling point of water at the reduced pressure; whereby at least some of the moisture in the rind explodes into steam, thereby fragmenting the rind. 
     
     
       6. A process for preparing a non-woven mat of cellulosic fiber bundles, comprising the steps of: (a) obtaining cellulosic fiber bundles by the process recited in claim 1; and   (b) allowing the fiber bundles to dry in contact with one another; whereby a non-woven mat of the fiber bundles is formed.     
     
     
       7. A non-woven mat of cellulosic fiber bundles produced by the process of claim 6. 
     
     
       8. A process for obtaining cellulosic fiber bundles at least 2.5 centimeters long from lengths of a plant stalk rind which has a high lignin content, wherein the rind comprises cellulosic fiber bundles comprising ultimate fiber cells which are substantially smaller than said fiber bundles, comprising the simultaneous steps of: (a) partially delignifying the rind; and   (b) subjecting the rind to limited mechanical action; wherein said partial delignifying step and said limited mechanical action step suffice to obtain cellulosic fiber bundles from the rind, but are insufficient to reduce the cellulosic fiber bundles to ultimate fiber cells; and   wherein sufficient lignin remains in the cellulosic fiber bundles following said partial delignifying step and said limited mechanical action step to bind the fiber cells into fiber bundles at least 2.5 centimeters long.     
     
     
       9. A process as recited in claim 8, wherein the plant from which the rind is derived is kenaf, bamboo, milkweed, or a bast fiber plant having a high lignin content. 
     
     
       10. A process as recited in claim 9, wherein the plant from which the rind is derived is kenaf. 
     
     
       11. A process as recited in claim 9, wherein said partial delignifying step comprises treating the rind with alkali and heat. 
     
     
       12. A process as recited in claim 8, wherein said limited mechanical action step comprises oscillatory agitation, vigorous boiling, rapid passage of gas bubbles through the rind, or passage through a rotating helical screw. 
     
     
       13. A process as recited in claim 8, wherein said partial delignifying step comprises treating the rind with alkali and heat; and wherein said limited mechanical action step comprises oscillatory agitation, vigorous boiling, rapid passage of gas bubbles through the rind, or passage through a rotating helical screw. 
     
     
       14. A process as recited in claim 8, wherein said limited mechanical action step comprises impregnating the rind with steam; and abruptly reducing the pressure applied to the rind, at a temperature above the boiling point of water at the reduced pressure; whereby at least some of the moisture in the rind explodes into steam, thereby fragmenting the rind. 
     
     
       15. A process for preparing a non-woven mat of cellulosic fiber bundles, comprising the steps of: (a) obtaining cellulosic fiber bundles by the process recited in claim 8; and   (b) allowing the fiber bundles to dry in contact with one another; whereby a non-woven mat of the fiber bundles is formed.     
     
     
       16. A non-woven mat of cellulosic fiber bundles produced by the process of claim 15. 
     
     
       17. A process for obtaining cellulosic fiber bundles at least 2.5 centimeters long from lengths of sugar cane rind containing moisture, comprising the steps of: (a) placing the rind in a closed reaction chamber, and heating the rind and the moisture in the rind under pressure to a temperature above 100° C.; and   abruptly reducing the pressure in the reaction chamber to one atmosphere or less, causing the explosion of at least some of the moisture in the rind into steam; wherein the steam explosion has a force which is sufficient to fragment the rind and to obtain cellulosic fiber bundles from the rind, but which is insufficient to reduce the cellulosic fiber bundles to ultimate fiber cells; and   wherein sufficient lignin remains in the cellulosic fiber bundles following the steam explosion to bind the fiber cells into fiber bundles at least 2.5 centimeters long.     
     
     
       18. A process for preparing a non-woven mat of cellulosic fiber bundles, comprising the steps of: (a) obtaining cellulosic fiber bundles by the process recited in claim 17; and   (b) allowing the fiber bundles to dry in contact with one another; whereby a non-woven mat of the fiber bundles is formed.     
     
     
       19. A non-woven mat of cellulosic fiber bundles produced by the process of claim 18. 
     
     
       20. A process for obtaining cellulosic fiber bundles at least 2.5 centimeters long from lengths of a plant stalk rind which contains moisture and which has a high lignin content, wherein the rind comprises cellulosic fiber bundles comprising ultimate fiber cells which are substantially smaller than said fiber bundles, comprising the steps of: (a) placing the rind in a closed reaction chamber, and heating the rind and the moisture in the rind under pressure to a temperature above 100° C.; and   (b) abruptly reducing the pressure in the reaction chamber to one atmosphere or less, causing the explosion of at least some of the moisture in the rind into steam; wherein the steam explosion has a force which is sufficient to fragment the rind and to obtain cellulosic fiber bundles from the rind, but which is insufficient to reduce the cellulosic fiber bundles to ultimate fiber cells; and   wherein sufficient lignin remains in the cellulosic fiber bundles following the steam explosion to bind the fiber cells into fiber bundles at least 2.5 centimeters long.     
     
     
       21. A process as recited in claim 20, wherein the plant from which the rind is derived is kenaf, bamboo, milkweed, or a bast fiber plant having a high lignin content. 
     
     
       22. A process as recited in claim 21, wherein the plant from which the rind is derived is kenaf. 
     
     
       23. A process for preparing a non-woven mat of cellulosic fiber bundles, comprising the steps of: (a) obtaining cellulosic fiber bundles by the process recited in claim 20; and   (b) allowing the fiber bundles to dry in contact with one another; whereby a non-woven mat of the fiber bundles is formed.     
     
     
       24. A non-woven mat of cellulosic fiber bundles produced by the process of claim 23.